1. Field of the Invention
The present invention pertains to a method and apparatus for performing cementing operations in oil or gas wells. More particularly, the present invention comprises a method and apparatus for performing cementing operations in oil or gas wells equipped with top drive systems and casing running tools. More particularly still, the present invention pertains to a method and apparatus for performing cementing operations in oil or gas wells using a plug dropping cement head on rigs equipped with top drive systems and casing running tools.
2. Brief Description of the Prior Art
Conventional rotary drilling rigs typically comprise a supportive rig floor incorporating a rotary table, a substantially vertical derrick extending above said rig floor, and a traveling block or other hoisting mechanism that can be raised and lowered within said derrick. During drilling or servicing operations, such rig equipment is often used to manipulate tubular goods, such as pipe, through the rotary table and in and out of a well bore extending into the earth's crust. Once a well has been drilled to a desired depth, large diameter pipe called casing is frequently installed in such well and cemented in place. The casing is typically installed to provide structural integrity to a well bore, and to keep geologic formations isolated from one another.
When conventional drilling rigs are used, casing is typically inserted into a well in a number of separate sections of substantially equal length. Single sections of pipe called “joints,” are typically screwed together or otherwise joined end-to-end at the rig in order to form a substantially continuous “string” of pipe that reaches downward into the earth's surface. As the bottom or distal end of the pipe string penetrates further into a well, additional sections of pipe are added to the ever-lengthening pipe string at the rig.
Conventional casing operations typically involve specialized crews and equipment mobilized at a rig site for the sole purpose of running casing into a well. With conventional casing operations, powered casing tongs, casing elevators and spiders, and at least one dedicated hydraulic power unit are typically required to be mobilized to a well location and installed just prior to such casing operating. Specialized casing crews must rig up and operate the equipment, connect the joints of casing to run in the well, and demobilize the equipment following completion of the job. During a conventional casing installation operation, the regular drilling crew usually plays a secondary role and typically just assists in the process.
Top drive systems, which can be used to pick up sections of pipe, connect such pipe sections together, and provide the torque necessary to drill wells, have been used on drilling rigs for some time to make-up drill pipe connections and to efficiently drill wells. However, until relatively recently, it has been a challenge to develop a viable method of using top drives systems to make-up and run casing strings, just as strings of drill pipe have historically been run.
A method of running casing using a rig's top drive system together with a casing running tool (CRT) has become increasingly popular in recent years. A drilling crew can run entire strings of casing more efficiently and for less cost than with conventional casing crews and equipment. CRT's can be used to pick up and stab single joints of casing, eliminating the necessity for personnel to be located at an elevated location on a rig, such as on the casing stabbing board. Because top drive systems can be used to provide torque to make up casing connections, specialized casing tongs are not required. Further, fewer personnel are needed on and around the rig floor during the casing running operations, resulting in faster and more efficient casing installation.
In most cases, a CRT is connected immediately below a rig's top drive unit prior to commencement of casing operations. A single-joint elevator, supported by a CRT, is typically used to lift individual joints of casing from a V-door or pipe rack to a well. In this manner, each joint of casing is stabbed into the previous joint (already installed in a well), and the top drive and attached CRT are lowered until the CRT covers the top of the new joint being added. The slips of the CRT are set on the joint of casing, and the top drive is actuated to apply the required torque (through the CRT) to make up the casing connection.
Cementing operations can be made more complicated by the use of CRT's and associated equipment. During such casing operations, a cement head is typically installed to provide a connection or interface between a CRT and a casing string extending into a well that must be cemented in place. Such cement heads should beneficially permit cement slurry to flow from a pumping assembly into a well, and should have sufficient flow capacity to permit high pressure pumping of large volumes of cement and other fluids at high flow rates.
Such cement heads should also have sufficient tensile strength to support heavy weight tubulars extending from the surface into a well, and to accommodate raising and lowering of such tubular goods without interfering with and/or intermittently stopping longitudinal and/or rotational movement of a casing string. It is frequently considered good practice to rotate and/or reciprocate a string of casing while such casing is being cemented in a wellbore in order to facilitate better cement distribution within the annular space between the outer surface of the casing and the inner surface of a well bore. Cement heads should also beneficially swivel in order to permit rotation of the tubular goods and/or other downhole equipment in a well while maintaining circulation from the surface pumping equipment into the down hole casing string extending into the well.
Darts, balls, plugs and/or other objects, typically constructed of rubber, plastic or other material, are frequently pumped into a well in connection with cementing operations. In many instances, such items are suspended within a cementing head until the objects are released or “launched” at desired points during the cement pumping process. Once released, such items join the cement slurry flow and can be pumped down hole directly into a well. Such darts, balls, plugs and/or other objects should be beneficially held in place within the slurry flow passing through the cement head prior to being launched or released without being damaged or washed away by such slurry flow.
In most cases, cement heads comprise multiple sections or “subs” that are connected using threaded connections. In order to ensure that such threaded connections form fluid seals that can withstand expected pressures, and that the joined components exhibit necessary tensile strength, such connections are typically made up at a facility or other staging location prior to transportation of a cement head to a rig or other work site. As a result, it is typically very difficult and time consuming to separate the various components of a cement head when access to the internal components of such cement head is required at a well location. Although there are many different reasons why such access may be required, common examples include the need to inspect plugs, darts, balls or other objects, or to reload such items within a cement head. Frequently, specialized equipment is needed to connect or disconnect the components of a cement head at a well location, making such operations expensive, inconvenient and/or otherwise undesirable.
Thus, there is a need for a cement head that permits cement flow into the cement head from above, and has a high tensile strength as well as the ability to rotate or swivel. Valves used to isolate or restrict flow through the cement head, as well as launching mechanisms for releasing darts, balls, plugs and/or other objects into the slurry flow, should be remotely actuated from a safe distance thereby eliminating the need for lifting personnel overhead. Audible and/or visual indicators should also be provided to alert personnel on or in the vicinity of the rig floor about the operation of various elements of the tool and/or the status of objects launched into a well.
Additionally, there is a need for a cement head that permits quick and efficient connection and/or disconnection of the major components of such cement head at a rig site or other remote location (such as, for example, when access to the internal components of the cement head is desired). Such connection and/or disconnection should be relatively quick and efficient, and should not require use of specialized equipment or excessive personnel.